This invention concerns primer compositions comprising aliphatic conjugated diolefin polymer with acrylic portion grafted thereon. These graft copolymers can impart high alkaline resistance to primer coatings.
Constituent monomers of this invention that are grafted onto the aliphatic conjugated diolefin polymer include etherified N-methylolacryamide monomers and acrylic functional monomers. Further, it is essential that the aliphatic conjugated diolefin polymer comprise a high content of 1,2 vinyl units.
U.S. Pat. No. 3,297,623 discloses graft copolymers comprising aliphatic conjugated diolefin polymer backbone that has grafted thereon certain methylol acrylamide monomers. U.S. Pat. No. 3,297,623, however, differs in several respects from the invention herein including, in particular, the use therein of aqueous latex grafting, lack of disclosure relating to high vinyl content as well as failure to include hydroxyfunctionality for enhanced crosslinking. Other graft copolymers possibly of interest are disclosed in U.S. Pat. No. 3,206,432 and U.S. Pat. No. 3,113,036, which, however, disclose graft copolymers with aliphatic conjugated diolefin polymers having high 1,4 addition configuration. Still another graft copolymer is disclosed in U.S. Pat. No. 3,639,216.
Certain etherified N-methylolacryamide monomers suitable herein for grafting have been disclosed as suitable for inclusion in acrylic copolymer coating systems as in U.S. Pat. No. 3,551,525. In that disclosure, however, no graft copolymers are made.
An aspect of this invention is that the graft copolymer made as hereinafter disclosed under certain non-aqueous solution polymerization conditions, further can be combined with additional aliphatic conjugated diolefin polymer to provide increased solids content yet not deleteriously detract from the physical properties of the cured film when properly formulated and cured. U.S. Pat. Nos. 3,170,805, 3,365,411 and 3,897,260 all relate to blended aliphatic conjugated diolefin resins but do not disclose the use of graft copolymers as herein.
Another aspect of this invention includes the use of additional crosslinking agents to improve the properties of the cured film. U.S. Pat. No. 3,223,655 discloses the use of graft copolymers containing an acrylic portion that is crosslinked with added crosslinker but the primers therein are said to be useful with a low content, e.g. 2-20% by weight aliphatic conjugated diolefin polymer. Similarly, U.S. Pat. No. 3,796,770 discloses an adduct of diene polymer and unsaturated carboxylic acid monomer that is crosslinked with added crosslinker but the monomer content is quite different than herein.
Still another aspect of this invention is the improvement in properties obtained through the inclusion of hydroxy functional silicones into the primer compositions. U.S. Pat. No. 3,318,971 and U.S. Pat. No. 3,468,836 disclose hydroxy silicones in coating compositions. These patents also disclose a special advantage of hydroxy functional silicones with, for example, certain N-methylolacryamide functionality. But these patents do not disclose the use of acrylic graft copolymers made with aliphatic conjugated diolefin polymers as herein for use with hydroxy functional silicones.